What is gravity really?

Because of gravity, if you drop something, it falls down, instead of up. Well, everybody knows that! But, what does this really mean? What is gravity?

Gravity has played a big part in making the universe the way it is. Gravity is what makes pieces of matter clump together into planets, moons, and stars. Gravity is what makes the planets orbit the stars--like Earth orbits our star, the Sun. Gravity is what makes the stars clump together in huge, swirling galaxies.

A great scientist, Albert Einstein, who lived in the 20th century, had a new idea about gravity. He thought that gravity is what happens when space itself is curved or warped around a mass, such as a star or a planet. Thus, a star or planet would cause kind of a dip in space so that any other object that came too near would tend to fall into the dip.

This 2-D animation gives an idea of how gravity works in 3-D.

Quite a number of experiments show that Einstein was right about this idea and a lot of others. But there are questions for which even Einstein had no answers.

For example, if gravity is a force that causes all matter to be attracted to all other matter, why are atoms mostly empty space inside? (There is really hardly any actual matter in an atom!) How are the forces that hold atoms together different from gravity? Is it possible that all the forces we see at work in nature are really different sides of the same basic force or structure?

Could some of the same laws of nature be at work in the designs of all things in the pictures above?

These are big questions that scientists and ordinary people like us have wondered about for a long time. For a long time we haven't known how to go about finding the answers, other than trying to work things out on paper.

But now NASA has a special program, called

. . . for seeking answers to these and other mysteries of the universe. Fundamental Physics hopes to do two things:

To discover and understand the basic rules nature uses to build the complex and beautiful structures we see around us.

Over the years, scientists and engineers have developed new technologies and instruments that will help us understand nature. Now we can take these new instruments into space and do experiments where the forces of gravity are very, very small (like when the Space Shuttle or the International Space Station are orbiting Earth in "free fall"). This way, scientists can do very delicate experiments to see what single atoms do under special conditions.

NASA hopes these experiments will help us understand our universe and ourselves. NASA also hopes the experiments will help develop technologies that will benefit people in their everyday lives.